Funds for a high-resolution freeze-fracture system and accessories are requested. The freeze-fracture machine must have 1) rotary stage capable of low temperature operation; 2) excellent temperature control for freeze-etch work; and 3) gun control power supply and guns capable of forming tantalum-tungsten replicas with reproducible thickness. These features are met in the Cressington CFE50 freeze-fracture system. The major user group comprises Drs Khan, Condeelis, B. Satir and P. Satir. Dr Khan will use the machine for quantitation of dimensions of the bacterial flagellar motor particles seen by freeze-fracture and for freeze-etch studies of flagellar basal assemblies. Dr Condeelis seeks to derive positional information on binding sites and peptide composition from rotary shadowed actin binding protein molecules. Dr P. Satir will conduct freeze-etch studies on the "necklace" and axonemes of motile and photoreceptor cilia. Dr B. Satir wants to follow the dispersal of the particles comprising secretion fusion "rosettes" during progress of exocytosis. These studies have as general theme the interaction of macromolecular protein assemblies with membranes for force production and signal transduction and seek to combine genetic, biochemical or immunological tools with structure determination. in addition, a group of 3 neuroscientists, Drs Bennet, Hall and Spray, and 3 molecular biologists, Drs Carrasco, Leinwand and Spudich will have access to the instrument. These investigators are asking structural questions in concert with molecular approaches that are consistent with the general theme. The neuroscientists seek to distinguish between different types of gap junction lattices through high resolution shadowing techniques. Drs Spudich and Carrasco will characterize and determine aggregation states of reconstituted receptor proteins in vesicles and Dr leinwand will conduct molecular shadowing studies of genetically altered myosins.